The present invention pertains to a fail-safe system, in particular, an electromechanical brake system which contains the following components:
an actuating device that can be moved into different positions from a starting position, PA1 three sensors that generate a measuring signal which corresponds to the position of the actuating device independently of one another, wherein the first of the three sensors is supplied with energy by a first independent energy source via a first supply path, and wherein the second of the three sensors is supplied with energy by a second independent energy source via a second supply path. PA1 an actuating device that can be moved into different positions from a starting position, and PA1 three sensors that generate a measuring signal which corresponds to the position of the actuating device independently of one another, wherein the first of the three sensors is supplied with energy by a first independent energy source via a first supply path, and wherein the second of the three sensors is supplied with energy by a second independent energy source via a second supply path, characterized by the fact that
A sensor that generates a measuring signal which corresponds to the position of the actuating device may, for example, consist of a displacement sensor that measures the distance from the starting position of the actuating device to an actuating position. However, such a sensor may also consist of a force sensor that measures the force required for moving the actuating device from the starting position into an actuating position. Other sensor designs would also be conceivable.
The invention is described below with reference to an electromechanical brake system. However, the invention may also be used in other fail-safe systems, e.g., in an electromechanical steering system. In an electromechanical brake system, the initially mentioned actuating device consists of the brake pedal. In this case, the driver decelerates the motor vehicle by exerting a certain force upon the brake pedal with the foot, wherein the effect of the force exerted upon the pedal is measured by sensors and converted into an electric signal. This signal is forwarded to brake actuators, one of which is assigned to each wheel of the motor vehicle. Each brake actuator exerts a braking force (that depends on the force exerted upon the brake pedal by the foot of the driver) upon the corresponding wheel of the motor vehicle with the aid of an electric motor.
DE 195 10 525 A1 discloses a method for controlling or regulating an electromechanical brake system of a motor vehicle. The electromechanical brake system contains a brake pedal, the actuation of which is measured by three sensors that operate independently of one another. The measuring signals generated by the sensors are forwarded to microprocessors of a computer system. Among other things, the measuring signals are checked for errors in the microprocessors. In addition, the nominal value for the braking force desired by the driver is determined in the microprocessors based on the measuring signals. This nominal value is adjusted in the electromechanical brake system by the microprocessors after calculations are completed.
The three sensors of the brake system known from DE 195 10 525 A1 respectively contain a separate energy supply. Consequently, if an energy source fails and the corresponding sensor is no longer supplied with energy, this does not interfere with the energy supply of the remaining sensors, i.e., two of three measuring signals are still generated. The microprocessors of the computer system are able to determine with the aid of a majority decision which of the three sensors has failed, wherein the brake system remains operative. The electromechanical brake system known from DE 195 10 525 A1 can still be designated as safe if one of the energy sources that supplies a sensor fails. However, this electromechanical brake system has a relatively complicated design due to the arrangement of three sensors that are respectively supplied by an independent energy source.
An object of the present invention is a fail-safe brake system that has a high safety standard despite a simple design.